The present invention relates to a diesel engine with a supercharger.
A diesel engine with a supercharger generally includes a heat exchanger in a supercharged air passage from an outlet port of the supercharger to an inlet port of a cylinder, and cools supercharged air that has pressure and temperature increased by the supercharger. As the heat exchanger, an air cooling type of heat exchanger with outside air as a heat exchange medium, or a water cooling type of heat exchanger with the cooling water as a heat exchange medium is generally used.
For example, Japanese Patent Laid-open No. 57-35116 and Japanese Patent Publication No. 3-4731 disclose xe2x80x9ca hybrid type of heat exchanger including a water cooling type of heat exchanger at an upstream side, and an air cooling type of heat exchanger at a downstream side, which has a bypass supercharged air passage with an on-off valve, in the order from an outlet port of a supercharger to an inlet port of a cylinderxe2x80x9d. It should be noted that the latter is an improvement over the former, and the latter has the configuration in which the water cooling type of heat exchanger at the upstream side together with the on-off valve is housed in an upper tank of the air cooling type of heat exchanger at the downstream side. This configuration provides the operation and effects that the upper tank is also used as the bypass supercharged air passage and thereby the compact diesel engine with the supercharger is provided.
The above conventional configurations, however, have the following disadvantages, which cannot make the engine as compact as expected.
(1) The temperature of cylinder intake air varies to a large extent according to the driving conditions (atmosphere temperature, engine load, and the like). The temperature of the cylinder intake air becomes extremely cold due to low-temperature atmosphere in cold regions, severely cold regions, and the winter season, and, for example, under medium and heavy load, an excess air ratio increases, whereby combustion efficiency increases, thereby producing excessive output power contrary to the intention. Further, since the temperature is low inside the cylinder under light load, poor ignition easily occurs, and thus it is difficult to operate engine with stability. On the other hand, in tropical regions and in the summer season, the temperature of exhaust gas rises due to high-temperature atmosphere under heavy load, thereby decreasing durability of the components constructing the engine. In addition to the above disadvantages, there is a heat balance problem of the engine main body corresponding to a change in engine load. Accordingly, with only an air cooling type of heat exchanger, the heat exchanger itself increases in size and the heat exchanger needs to be provided with an air flow adjusting mechanism such as a large shutter or the like, thus making the heat exchanger system itself larger in size. Meanwhile, with only a water cooling heat exchanger, a large quantity of cooling water is needed, thus making a cooling system such as a cooling radiator and the like larger in size. Specifically, the water cooling type of heat exchanger alone or the air cooling type of heat exchanger alone is unfavorable in making the engine compact.
(2) As for the temperatures of outside air, cooling water, and supercharged air at the supercharger outlet port during normal rotation of the engine, the temperature is higher in the order of xe2x80x9cthe outside air temperature less than the cooling air temperature less than the supercharged air temperature at the supercharger outlet portxe2x80x9d. The aforementioned xe2x80x9cduring normal rotation of the enginexe2x80x9d means xe2x80x9cafter the starting of the engine, and during the rotation of the engine after the completion of warming-up, that is, during rotation of the engine irrespective of a low idle or a high idle, and the magnitude of loadxe2x80x9d. In the aforesaid conventional hybrid type of heat exchanger, the water cooling type of heat exchanger is provided at the upstream side, and therefore the engine cooling water is heated by a high-temperature supercharged air. Consequently, a large amount of cooling water is required to secure heat balance of the engine body corresponding to a change in engine load, whereby the radiator for cooling water and the like are made larger in size and the cooling system increases in size. Namely, even with the aforesaid conventional hybrid type of heat exchanger, the engine cannot be made as compact as expected.
(3) As for a diesel fuel, light oil is generally used, but fuels inferior to light oil in ignitability with normal compression ratio, for example, fuel oil A, a waste plastic oil fuel, a water emulsion fuel (fuel made by mixing fuel and water and emulsifying the same) and the like are sometimes used. Explaining with the water emulsion fuel as an example, as seen from the actual measurement results of the three types of engines shown in FIG. 10, this fuel has an effect of reducing injurious materials such as nitrogen oxides, black lead and the like, which are exhausted from a diesel engine, as a result of increasing content of water in the fuel. However, if the amount of water is increased in the above fuel, the aforesaid disadvantage (specifically, xe2x80x9cabnormal combustion easily occurs in the cylinder, which makes it difficult to operate the engine with stabilityxe2x80x9d) is promoted when the temperature of intake air of the cylinder is low (in cold regions, in severely cold regions, in the winter season, and under light load, etc.). When the content of water reaches 50%, the operation becomes unstable even at a room temperature. This is because water in the water emulsion fuel injected during the compression stroke of the engine vaporizes and the temperature inside the cylinder is reduced by the latent heat, whereby ignition and combustion of the water emulsion fuel (that is, engine performance) are hindered.
The present invention is made in view of the aforesaid disadvantages, and its object is to provide a diesel engine with a supercharger, which is capable of contributing to reduced engine in size, and which hardly has an adverse effect on the engine performance even with use of a fuel inferior to light oil in ignitability with a normal compression ratio.
In order to attain the above object, a first configuration of a diesel engine with a supercharger according to the present invention is
a diesel engine with a supercharger including a supercharger for taking in and pressurizing outside air and supplying the pressurized supercharged air into a cylinder, and a heat exchanger, which is provided in a supercharged air passage from an outlet port of the supercharger to an inlet port of the cylinder and cools the supercharged air from the supercharger, and
the heat exchanger is a hybrid type of heat exchanger including
a first heat exchanger for carrying out heat exchange between the supercharged air from the outlet port of the supercharger and a first heat exchange medium, and
a second heat exchanger for carrying out heat exchange between the supercharged air from an outlet port of the first heat exchanger and a second heat exchange medium having higher temperature than the first heat exchange medium, and supplying the supercharged air after the heat exchange with the second heat exchange medium to the cylinder.
As a second configuration of the diesel engine with the supercharger, a fuel used may be a water emulsion fuel.
As a third configuration of the diesel engine with the supercharger, the engine may be a water cooling type of engine with use of cooling water,
the first heat exchange medium is outside air, and
the second heat exchange medium is cooling water from the water cooling type of engine.
As a fourth configuration of the diesel engine with the supercharger, it may be suitable to further include load detecting means for detecting load of the engine, and
control means for receiving a detection signal from the load detecting means and controlling flow of the second heat exchange medium or flow of cooling water from the water cooling type of engine.
As a fifth configuration of the diesel engine with the supercharger, it may be suitable that the engine (or the water cooling type of engine) is used at an almost constant engine speed, and the diesel engine with the supercharger further includes
a pressure sensor which is provided between an outlet port of a compressor of the supercharger and an inlet port of the cylinder and detects supercharged air pressure, and
control means for receiving a detection signal from the pressure sensor and controlling flow of the second heat exchange medium or flow of cooling water from the water cooling type of engine.
A sixth configuration of the diesel engine with the supercharger according to the present invention is in a diesel engine with a supercharger including a supercharger for taking in and pressurizing outside air and supplying the pressurized supercharged air into a cylinder, and a heat exchanger, which is provided in a supercharged air passage from an outlet port of the supercharger to an inlet port of the cylinder and cools the supercharged air from the supercharger,
a fuel used is a fuel inferior to light oil in ignitability, and
means for maintaining temperature of the supercharged air supplied to the cylinder at a predetermined value is included.
The operations and effects of the above first to sixth configurations will be explained.
(1) As for the choice of the heat exchange medium, outside air, tap water (for example, in the case of stationary type of diesel generator engine), cooling tower cooling water (for example, in the case of stationary type of diesel generator engine), seawater (for example, in the case of a shipboard engine), engine lubricant oil, engine cooling water (for example, in the case of a water cooling type of engine), and the like can be cited as examples. When the choice of the heat exchange mediums during normal rotation of the engine is divided in two according to the degree of temperature, outside air, tap water, cooling tower cooling water and seawater are at a lower temperature side; and lubricant oil and cooling water are at a higher temperature side. Specifically, in the first configuration, outside air, tap water, cooling tower cooling water, and seawater correspond to the first heat exchange medium, while lubricant oil and cooling water correspond to the second heat exchange medium.
Thus, based on the first configuration, if supercharged air of high temperature is cooled by the outside air, tap water, cooling tower cooling water, and seawater which are the choice of the first heat exchange mediums, the temperature of the supercharged air after being cooled becomes lower than that of the lubricant oil and the cooling water which are the choice of the second heat exchange mediums according to a normal design. Specifically, the supercharged air cooled in the first heat exchanger is heated thereafter by the lubricant oil and cooling water which are the choice of the second heat exchange mediums in the second heat exchanger. The temperature of the second heat exchange medium does not change to a large extent. Hence, the temperatures of intake air of the cylinder converge on a narrow range less than or equal to the temperature of the lubricant oil and the cooling water irrespective of the temperature of outside air and load on the engine. Further in this situation, the second heat exchanger works as a cooler for the lubricant oil and cooling water. Accordingly, a lubricant oil system and a cooling water system, which are heat balance sources for a change in engine load are made compact, which specifically contributes to the engine itself reduced in size.
Even if the temperature of supercharged air after being cooled by the first heat exchanger is higher than those of the lubricant oil and the cooling water, the lubricant oil and cooling water, which are the choice of the second heat exchange mediums, cool the supercharged air once again. In this situation, the second heat exchanger works as a heater for the lubricant oil and cooling water, but the heat exchange amount is small in general. In this situation, basic heat balance of the engine main body corresponding to a change in engine load is not adversely influenced to a large extent, and therefore reduction in the size of the lubricant oil system and the cooling water system, specifically, reduction in size of the engine itself is not hindered.
Specifically, according to the first configuration, the diesel engine with the supercharger equipped with a highly efficient supercharged air cooling mechanism is provided. Naturally, it is not necessary to provide xe2x80x9ca bypass supercharged air passage with an on-off valvexe2x80x9d as in the conventional hybrid type of heat exchanger, which also contributes to the reduction in the size of not only the supercharged air cooling mechanism but also the engine itself.
(2) The second configuration has the aforesaid operation and effects of the first configuration that xe2x80x9cthe temperatures of intake air of the cylinder converge on a narrow range less than or equal to the temperature of the lubricant oil and the cooling water irrespective of the temperature of outside air and load on the enginexe2x80x9d. Accordingly, even if a water emulsion fuel is used as a fuel used, or even if the quantity of water in the water emulsion fuel is large, abnormal combustion hardly occurs in the cylinder, and stable engine operation can be performed. As a result of the experiments, it is confirmed that a stable operation can be performed even if the water content in the fuel exceeds 50 volume %. Thus, injurious materials such as nitrogen oxides, black lead and the like exhausted from the engine can be reduced without adverse effects given to the engine performance.
(3) The outside air being the first heat exchange medium and the cooling water being the second heat exchange medium in the third configuration are examples of the choice of the heat exchange mediums mentioned in the description of the operations and effects of the first configuration. Consequently, according to the third configuration, the operation and effects based on the first configuration can be obtained as they are.
(4) According to the first to the third configuration, xe2x80x9cthe temperatures of intake air of the cylinder converge on a narrow range less than or equal to the temperature of the lubricant oil and the cooling water irrespective of the temperature of outside air and load on the enginexe2x80x9d as described in the operation and effects of the first configuration, but in the fourth configuration, the control means for controlling the flow of the second heat exchange medium (or the flow of the cooling water from the water cooling type of engine) supplied to the second heat exchanger according to the load of the engine is provided. As a result, when the load is heavy, the flow of the second heat exchange medium is stopped or reduced, whereby supercharged air sufficiently cooled is supplied to the engine to thereby secure output power. When the load is light, the flow of the second heat exchange medium is increased to the full-throttle level, or just increased, whereby supercharged air is warmed to ensure ignition of the engine, thus making it possible to decrease discharge amount of white smoke and reduce variation of the rotational frequency.
(5) If the engine speed is almost constant, positive correlation exists between the load of the engine and the supercharged air pressure. In the fifth configuration, based on the first to third configurations, control means for controlling the flow of the second heat exchange medium ((or the flow of the cooling water from the water cooling type of engine) in accordance with supercharged air pressure of the engine is provided. As a result, the flow of the second heat exchange medium supplied to the second heat exchanger is controlled in accordance with supercharged air pressure of the engine (specifically, the load of the engine), thereby making it possible to obtain the same operation and effects as in the fourth configuration.
(6) The sixth configuration is higher conceptualization of the fourth configuration citing the second configuration. In concrete, xe2x80x9ca water emulsion fuelxe2x80x9d is xe2x80x9ca fuel inferior to light oil in ignitabilityxe2x80x9d, and xe2x80x9cload detecting means and control meansxe2x80x9d are xe2x80x9cmeans for maintaining the temperature of supercharged air supplied to the cylinder at a predetermined valuexe2x80x9d. Accordingly, each operation and effect described in the operations and effects in the second and fourth configuration can be obtained.